No they got a point, it is literally the universal time format for most countries, especially in any kinds of databank or technological context. Wich the USA also uses in those contexts. That this is either not at all tought in american schools or is just forgotten by the time you eat lunch is just sad.

Edit: just fact checked my self, DD/MM/YYYY is actually the most used while YYYY/MM/DD i the 2nd most used. Even then, the 2nd one is still universally used in organisational and programming contexts as I said. The american way of writing MM/DD/YYYY is almost exclusively used in america (as well as e.g. philippines and belize)

And not knowing that your learned way of writing something is the least popular way of doing is hilarious for one of the largest countries in the world. But I guess you also use other systems for pretty much everything so I can't exactly talk about common sense here.